U.S. Pat. No. 5,217,080, entitled "Sealing System for a Sealed bearing assembly" which issued to Kenneth Hugo Wenzel and Dean Foote on Jun. 8, 1993 discloses a sealed bearing assembly for use in earth drilling in which the pressure drop across the bit due to jetting is sealed by a centrally positioned mechanical seal. This is accomplished by having a lubricant filled first chamber above the mechanical seal pressurized by a floating piston and a second chamber below the mechanical seal in communication the annulus such that drilling fluids from exterior of the tool enter the second chamber. A second floating piston is in communication with drilling fluids in the second chamber and provides pressure balancing to equalize pressure in a sealed chamber sealed at a lower or bit end by a fixed seal.
U.S. Pat. No. 5,217,080 while representing an advance over the prior art has two inherent disadvantages. One disadvantage is that according to its teachings corrosive drilling fluids are allowed to enter into the interior of the tool. The presence of corrosive drilling fluids requires that the exposed components be specially treated or made of corrosion resistant materials such as stainless steel. Another disadvantage is the length of the tool. In directional drilling, it is desirable to have the downhole drilling motor assembly as short as possible in order to facilitate making tight radiused turns to "build angle" as rapidly as possible.